Currently, there are two main systems in the market for correcting the position of teeth. The first system is a braces scenario that may include traditional self-ligating orthodontic brackets with a steel tight bracket, a straight wire application, or a traditional Tweed appliance. The second system is a clear aligner system, in which aligners are interchangeable by the patient during treatment. The clinician may prescribe a series of aligners, which are generally placed over, but are not themselves adhesively secured or otherwise attached to, the patient's teeth, to move one or more teeth from their original position to their aesthetically pleasing or functionally corrected position. Typically, a series of aligners is required to fully treat the patient because the degree of movement produced by a given single aligner is limited. One such aligner system is the INVISALIGN aligner system (Align Technology, Inc., San Jose, Calif.). Each aligner is responsible for moving the teeth toward their final pre-determined or aesthetically/functionally correct position.
The INVISALIGN aligners are fabricated by physical and computer-aided molding processes. The conventional process begins by taking an impression of the patent's dentition, or using intra-oral scanner for teeth impression, followed by creating a denture model of the teeth on computer. This CAD file, for example an .STL file, is used to 3D-print the physical teeth models and molds. Finally, clear plastic which will form the aligner, such as a polyurethane, is molded (e.g., thermoformed) over the physical teeth model or mold of the tooth configuration to be implemented. Subsequent physical steps of the conventional process trim the molded aligner to remove sharp edges or portions which might contact and irritate the gingiva. In addition, the aligner surface and edges are typically smoothed via a process such as tumbling.
This conventional fabrication of aligners is a tedious process, which compounds both cost and time of treatment for the patient. Since such an orthodontic treatment may require, for example, 25 intermediate reset molds to represent 25 stages of treatment progress, the cost and time required for the necessary steps of mold making, aligner formation, and trimming, may be prohibitively high. The cost is additive, as each new stage in treatment or each change in treatment requires the production of a new mold. Likewise, the cost of storing a series of molds for each patient throughout treatment may be formidable. U.S. Pat. No. 5,975,893 to Align Technologies, Inc., is incorporated by reference herein in its entirety, to describe the processes elaborated above, as background information.
Treatment of malocclusion by aligners faces challenges other than the difficulty of manufacture. Specifically, aligners fastened with attachments may prove very difficult to install, as a result of the limited number of shapes that the attachment apertures on the aligner may take, consistent with the INVISALIGN manufacturing process. Specifically, the attachment apertures are formed by thermoforming over a stereolithographically-generated positive tooth model, which limits the type of apertures that may be made. Moreover, aligners may bind with the attachments and prove very difficult to remove. Furthermore, in many aligner patients, the presence of the aligner within the patient's mouth causes a change in the points of occlusion between the mandible and maxilla, and in particular, causes the guidance of occlusion to move to the rear molars. This opens the patient's bite and typically intrudes the rear molars as a consequence of the unbalanced occlusion force on the rear molars.
One result of this conventional unbalanced occlusion force can be TMJ injury after the removal of the aligner, because the force of the mandible is no longer resisted by the rear molars in the absence of the aligners. For many patients aligners fabricated manually or by thermoforming on a positive model are uncomfortable and can irritate the patient's gingiva and/or tongue to such an extent that the soft tissue becomes inflamed and can potentially bleed. This discomfort is generally caused because the aligner is trimmed inaccurately to the patient's gingival margin. The inaccuracy in trimming is generally caused by the minimum size of the trimming tool particularly on the anterior lingual side where the aligner interferes with the tongue. Other anatomy such as the incisive papilla, if not generally considered when trimming the aligner, can cause swelling or inflammation. In addition, the location where the aligner is trimmed can cause a sharp flange to be created at the base of the aligner near the gingival margin, particularly on the lingual side.
Due to disadvantages of thermoforming and to reduce the steps involved in conventional aligner manufacturing methods, as well as aligner design limitation of thermoforming process, an alternative method is needed to manufacture an aligner to configure better to the counters of the teeth and to provide better finishing of the appliance. This would reduce the inaccuracy of each step to provide better adaptation, better fit, and better finish.
An ideal alternative apparatus and methodology for realizing aligners configured to correspond to a series tooth configurations should be economical, reusable, reduce time consumption, reduce material waste, and in particular, should reduce the need for fabricating multiple casts of teeth arrangements for various stages in the orthodontic treatment.